1. Field of the Invention
The present invention relates to multistage amplifiers having automatic gain control and more particularly to an amplifier having a gain incrementable in binary steps according to the relationship G = (A).sup.n where A is any number and n is any integer, and in which the number of stages of amplification corresponds to the number of digits in a binary number while the number of gain increments corresponds to all of the binary numbers countable from the number of binary digits employed. The present invention also relates to magnetic tape readback data decoding and more particularly to a decoding circuit in which data errors resulting from noise in the interblock gap periods and from decoded data having signal amplitudes below that required for accurate decoding, are eliminated,
2. Description of the Prior Art
Automatic gain control amplifiers of the prior art have a gain which is variable in accordance with variations in the input signal applied thereto. This presents a problem in data decoders in which the decoded data signal level must remain level, when the input signal level is variable as occurs in magnetic tape readback systems. The gain of such prior art AGC amplifiers is not constant over particular ranges of input signal amplitudes, but rather varies continuously. In accordance with the present invention, a simple, accurate and inexpensive amplifier is disclosed in which the gain thereof is initially set at any one of a number of possible levels in accordance with the characteristics of the particular tape to be read, and variation of data signal amplitude will not vary the amplifier gain once set.
A data decoding system of the prior art is disclosed by U.S. Pat. No. 3,715,738, wherein data signal peaks are sensed and compared with threshold levels to produce data pulses which correspond to the sensed signal peaks. This signal is also compared to the data clipping levels to produce gating pulses when the clipping levels are exceeded.
An AGC amplifier of the prior art is disclosed by U.S. Pat. No. 3,660,821, in which the tape preamble data is coupled to the amplifier to set the amplifier gain, which may then be intermittently varied in accordance with a predetermined reference level.
Another problem of prior art AGC amplifiers is their complexity and low peak to peak output voltage swing when integrated circuit design is used. The present invention has a number of gain increments that are exponentially related to the number of stages of amplification, with each increment being binarily related to the other increments.